1. Field of the Invention
The present invention relates to a method of forming barrier ribs of a display panel, particularly a method of forming barrier ribs in a display area for fabrication of a display panel such as a plasma display panel (PDP).
2. Description of the Related Art
Thin display panels such as PDP, LCD and FED are used in various fields. In particular, the PDP which exhibits an excellent visibility and a high display speed is suitable for high-definition display, for example, what is known as high-vision in JAPAN.
The PDP is a self-luminous display panel which has a discharge space defined by a pair of substrates (typically, glass plates) spaced a minute distance in an opposing relation with the periphery thereof being sealed.
In general, PDPs employing a matrix display system include barrier ribs having a height of about 100 .mu.m to about 200 .mu.m for partitioning the discharge space. For examnle, a PDP of a surface discharge type suitable for fluorescent color display includes linear barrier ribs equidistantly arranged across lines for matrix display. The spacing between adjacent barrier ribs (inter-rib spacing) is, for example, about 200 .mu.m for a 21-inch color PDP. The barrier ribs prevent discharge coupling and color cross-talk between adjacent cells.
In recent years, a dry etching technique has been replaced with a pattern printing technique for the formation of the barrier ribs. Exemplary dry etching processes hitherto known include a sand blast method and a hydro-honing method. In the sand blast method, a uniform rib material layer (plain film) is formed on a substrate and then a cutting mask having a predetermined pattern is formed thereon by photolithography. Thereafter, the rib material layer is patterned by jetting thereto particles as a cutting medium. In the hydro-honing method, a liquid as a cutting medium is jetted to the rib material layer for the patterning thereof. The sand blast method and the hydro-honing method are suitable for the formation of barrier ribs in a large display screen in terms of productivity, and exhibit a higher patterning accuracy than a wet etching method. In particular, the sand blast method is often employed because of its convenience.
In a conventional practice, the cutting mask pattern has substantially the same configuration as that of a rib pattern, except that a predetermined margin is added to the dimensions of the rib pattern in consideration of the contraction of the rib material during annealing after the removal of the rib material layer. That is, the cutting mask has a configuration similar (or conformable) to that of the rib pattern as viewed in plan.
An attempt has been made to form barrier ribs having reduced dimensions for higher definition by using such a cutting mask. Where the inter-rib spacing is reduced to the extent of about 100 .mu.m, however, an inconvenience often occurs such that the barrier ribs are partially lost during the sand blast process. That is, the incidence of patterning defect is drastically increased.
One method for preventing such a patterning defect is as follows. A protecting mask is provided on outer periphery of ends of the cutting mask to block an air flow along the length the barrier ribs during the rib-material cutting process, thereby preventing excessive removal of end portions of the barrier ribs (see Japanese Unexamined Patent Publication No. HEI 7(1995)-45193). However, a proper dimensional control of the protection mask is difficult where unnecessary rib portions should not exist around intended barrier ribs in a display panel. In the PDP, for example, the unnecessary rib portions obstruct an evacuating process and, therefore, the protection mask should be so designed that the unnecessary rib portions below the protection mask can be completely removed at the end of the rib-material cutting process. In addition, this method is not effective for prevention of the widthwise side-cut of the barrier ribs, so that the patterning defect cannot be perfectly prevented.